The present invention relates to a method of attaching one or more components to a connection support. It relates in particular to the interconnection and packaging of electronic components or electro-optical components.
Various types of connection supports are known. A first type of support, referred to as an xe2x80x9cinterconnection supportxe2x80x9d, is intended to receive a plurality of components. It is used as a component interconnection means, for example for forming electronic circuits. Another type of support, referred to as an xe2x80x9cintermediate supportxe2x80x9d, is generally combined with the component in its packaging. The role of the intermediate support is in essence to adapt the small pitch of the connection terminals of one or more components to the broader pitch of the printed circuit boards. Another role of intermediate supports is to reduce the stresses due to differences in coefficients of thermal expansion between the components and the interconnection supports, or between the components and the printed circuit boards.
The invention thus finds applications in the field of electronics and optoelectronics in particular for the interconnection of components and/or their packaging. The invention concerns in particular components for portable telephones.
Documents (1) to (10), whose complete references are given at the end of the description, describe various known techniques for the electrical and mechanical connection of components.
Among these techniques there are in particular the attachment of components by balls of fusible material. This technique, also referred to as xe2x80x9cFlip Chipxe2x80x9d, consists of covering connection terminals of a component, or the reception terminals of a support substrate, with a material with a low melting point. This material is generally in the form of protrusions or balls. After having disposed the component on the support substrate, having taken care to make the corresponding terminals coincide, the fusible material is heated to be shaped and weld the contact terminals to the reception terminals. This is welding where the fusible material constitutes an added material.
The melting of the fusible material can be caused by heating the assembly formed by the component and the support, covered with balls. This is the case in particular when the melting point is sufficiently low not to alter the component. On the other hand, when the component is fragile, the fusible material of the balls can also be heated locally, for example by means of a laser beam.
The technique of connection by balls of fusible material requires a relatively large number of process steps. It is necessary in fact to provide the component and the connection support with pins, which are isolated from each other and which are made from a material which can be wetted by the fusible material. It is then necessary to cover the pins with fusible material and finally it is necessary to proceed with the welding per se.
In addition, the balls of fusible material maintain a certain spacing between the component or components and the connection support. This spacing may, in some cases, impair the compactness of the component and there is a risk that it may be prejudicial to good protection thereof.
Finally, the addition material for the welds, such as the fusible material, and the bonding layers receiving the fusible material, are liable to contain lead, which is harmful to the environment.
It is an object of the present invention to propose an attachment method which does not present the difficulties or limitations mentioned above.
One object of the invention is in particular to propose a simple and economical attachment method which makes it possible to reduce the number of operating steps.
Another object of the invention is to propose a method which avoids the use of lead.
Another object of the invention is to propose a packaging of the components which is particularly compact and reliable.
To achieve these objects, the invention has more particularly for its aim to provide a method of attaching at least one component provided with a plurality of electrical connection terminals, to a connection support, in which:
a) a connection support is provided, made of a material transparent to at least one wavelength of a laser beam, and having at least a first face with reception terminals matching the connection terminals of the component, the reception terminals comprising a material able to be welded to the connection terminals of the component without the addition of material,
b) the component is disposed on the first face of the connection support, making the connection terminals of the component coincide with the reception terminals of the support,
c) the connection terminals of the component are welded to the reception terminals of the support by applying a welding laser beam to the reception terminals through the transparent material of the support.
The use of a transparent material for the support makes it possible to access the reception terminals with precision and to apply thereto the energy necessary for welding. It should be emphasized that, in the case of the invention, the welding is a direct welding of the material or materials of the reception terminals to the material or materials of the connection terminals. In other words, no fusible material, or addition metal, is previously put in place on the terminals.
The material of the terminals can be chosen preferably from among: nickel, iron, and/or alloys thereof. These materials have the particularity of being able to be heated greatly in a localized fashion by means of the laser beam. A rapid welding can then be effected without a large quantity of heat being emitted to the connection support. This makes it possible to use relatively fragile materials for the support. Moreover, the weld remains limited solely to the parts of the reception and contact terminals which have been subjected to the laser beam.
For supports which are not very sensitive to heat, other materials can of course be used for producing the contact or reception terminals.
The welding of the reception terminals to the connection terminals can be a step by step welding. In this case, the various pairs of facing terminals are welded one after the other. The use of a laser beam in fact allows welding of about one microsecond long. As an alternative, the welding of several pairs of terminals can also be concomitant. This can take place while having recourse, for example, to holographic techniques for subjecting the support to the laser according to a holographic pattern corresponding to the terminals.
The invention can, as indicated in the introductory part, be used to advantage both for the interconnection of various components and for the packaging of the components.
In the first case, that is to say that of the interconnection of components, it is possible to attach a plurality of components to the same support provided with connection tracks selectively connecting various reception terminals together.
The connection tracks can thus electrically connect together terminals of the same component or different components. They can also serve to connect the components to power supply sources and/or signal input/output terminals provided on the connection support.
In the applications relating to the packaging of components, the method of the invention can be used to attach the components to intermediate supports. As mentioned in the introductory part, the intermediate supports can have a role of protecting the components, a role of redistributing the contact terminals in order to adapt the pitch thereof to a reception support, and finally a role of reducing the mechanical stresses due to differences in coefficients of thermal expansion in the parts in mechanical contact.
In particular the material of the intermediate connection support can be chosen with a coefficient of expansion higher than that of the component, and lower than that of a final reception support to which the component, provided with the intermediate support, must be attached. The connection support used as an intermediate support may advantageously be produced from a material of the sol-gel type. The coefficient of thermal expansion of these materials can in fact easily be controlled. In addition, the sol-gel materials allow the formation of a connection support whose face that is turned towards the component at least partly adopts the shape. An intermediate support of the sol-gel type can serve, for example, to effect an embedding of the component.
The intermediate support can have on its face opposite to the component a plurality of secondary terminals connected respectively to the reception terminals, for example by means of metallized holes. The pitch of the secondary terminals can be adapted to a final connection support for which the component is intended.
According to a particular implementation of the method, the secondary terminals can also be offset with respect to the reception terminals in a plane parallel to the first and second faces. This allows the application of a welding beam through the second face and perpendicular thereto. In this case, the beam passes through a minimum thickness of the support.
In order to obtain a plurality of components associated individually with intermediate supports, the components coming from the same primary substrate can be attached to a connection support and then, after the attachment, the primary substrate and the connection support can be cut in a concomitant fashion. This cutting then makes it possible to define the components, respectively fixed to connection support parts whose dimensions are adjusted to the components. An individual attachment of each component to an intermediate support does, however, remain possible.
Finally, the invention concerns a device comprising at least one component with connection terminals and a connection support with reception terminals. In accordance with the invention, the connection support is transparent to light and the reception terminals are directly welded against the connection terminals.